Field of the Invention
The present invention relates to a plate-shaped elastic vibrator of a linear driving vibration wave motor, and relates to a driver utilizing the above-described vibration wave motor.
Description of the Related Art
Heretofore, ultrasonic motors characterized by small size, light weight, and high-speed and silent driving have been adopted in lens barrels of imaging devices, and so forth. For example, a linear driving ultrasonic motor is disclosed in FIGS. 8(a) to 12(c) of Japanese Patent Application Laid-Open No. 2015-35947. The ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2015-35947 controls the phase difference between AC voltages applied to two phases of a piezoelectric element, thereby achieving an operation in a wide speed range. Moreover, a vibration wave driver prepared in consideration of the stiffness of a vibrator is disclosed in FIG. 6 of Japanese Patent Application Laid-Open No. 2006-115559.
Recently, the demand has been increased more and more for reducing the size of an electronic device in which an ultrasonic motor is mounted, particularly, for reducing the size of a lens driver. To achieve the reduction in the entire size of such a lens driver as shown in FIG. 12(b) of Japanese Patent Application Laid-Open No. 2015-35947, a vibrating plate of the ultrasonic motor is required to shorten a vibrating plate length L5 in a moving direction of the ultrasonic motor. However, simply uniformly shrinking the entire vibrating plate decreases the area of a piezoelectric element, and decreases the deformation attributable to the piezoelectric effect, thereby lowering the vibration amplitude. Moreover, reducing the entire dimensions of the piezoelectric element and the vibrating plate increases the resonance frequency, thereby further lowering the vibration amplitude. These consequently cause the thrust force of the ultrasonic motor to decrease. Hence, there is a limit to the shortening of the vibrating plate length L5 in the moving direction of the ultrasonic motor.